A non-aqueous secondary battery comprising a non-aqueous electrolyte solution is typically characterized by light weight, high energy, and long life, and it has been widely used as a source for portable electronic devices such as notebook computers, mobile phones, digital cameras, and video cameras. In addition, with transition to a society with less environmental burden, such a non-aqueous secondary battery has attracted attention as a source for hybrid electric vehicles (hereinafter abbreviated as “HEV”) and plug-in hybrid electric vehicles (hereinafter abbreviated as “PHEV”), and also in the field of power storage such as a power storage system for residence.
When a non-aqueous secondary battery is applied to vehicles such as automobiles and power storage systems for residence, materials excellent in terms of chemical or electrochemical stability, strength, corrosion resistance, etc. are required as constituent materials for the battery, from the viewpoint of cycling performance and long-term reliability under a high temperature environment. Moreover, the use conditions of such a non-aqueous secondary battery are largely different from those of a source for portable electronic devices, and the non-aqueous secondary battery must work even in a cold region. Accordingly, high-rate performance and long-term stability under a low temperature environment are also required as physical properties necessary for the non-aqueous secondary battery.
By the way, from the viewpoint of practical use, a non-aqueous electrolyte solution is desirably used as an electrolyte solution for a lithium ion secondary battery that works at an ordinary temperature. An example of a common solvent used therefor is a combination of a high-dielectric solvent such as a cyclic carbonate with a low-viscosity solvent such as a lower acyclic carbonate. On the other hand, a common high-dielectric solvent has a high melting point, and thus, it may cause deterioration of the low-temperature properties of an electrolyte used, depending on the type of the electrolyte solution. As a solvent capable of solving this problem, there has been proposed a nitrile solvent having a good balance between viscosity and relative dielectric constant. Among others, acetonitrile has been known as a solvent having prominent performance. However, since these solvents containing a nitrile group are seriously disadvantageous in terms of electrochemical reductive decomposition, several improvement plans have been reported.
For example, Patent Documents 1 and 2 disclose that a cyclic carbonate such as ethylene carbonate is mixed with a nitrile solvent such as acetonitrile and diluted so as to prepare an electrolyte solution with a reduced influence by reductive decomposition. Moreover, Patent Document 2 to 4 disclose that a negative electrode having a potential higher than the reduction potential of a nitrile solvent is used to produce a battery, in which the reductive decomposition of the nitrile solvent is suppressed. Furthermore, Patent Document 5 discloses a non-aqueous electrolyte solution, in which sulfur dioxide and one or more other aprotic polar solvents are added to a nitrile solvent for the purpose of forming a protective film on a negative electrode.